U.S. patent application number 15/840439 was filed with the patent office on 2018-06-21 for method and acoustic system for determining a direction of a useful signal source.
The applicant listed for this patent is SIVANTOS PTE. LTD.. Invention is credited to HOMAYOUN KAMKAR-PARSI, MARKO LUGGER.
Application Number | 20180176694 15/840439 |
Document ID | / |
Family ID | 60327167 |
Filed Date | 2018-06-21 |
United States Patent
Application |
20180176694 |
Kind Code |
A1 |
KAMKAR-PARSI; HOMAYOUN ; et
al. |
June 21, 2018 |
METHOD AND ACOUSTIC SYSTEM FOR DETERMINING A DIRECTION OF A USEFUL
SIGNAL SOURCE
Abstract
A method determines a direction of a useful signal source in an
acoustic system that has a first input transducer and a second
input transducer. The first input transducer generates a first
input signal from a sound signal from the surroundings and the
second input transducer generates a second input signal from the
sound signal. The first input signal and the second input signal
are used to form a plurality of angle-dependent directional
characteristics having a respective fixed central angle and a
respective given angular expansion. The signal components
pertaining to the individual directional characteristics are
examined for the presence of a useful signal from a useful signal
source. The applicable central angle is assigned to a useful signal
source ascertained in a particular directional characteristic as
the direction of the useful signal source.
Inventors: |
KAMKAR-PARSI; HOMAYOUN;
(ERLANGEN, DE) ; LUGGER; MARKO; (ERLANGEN,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SIVANTOS PTE. LTD. |
Singapore |
|
SG |
|
|
Family ID: |
60327167 |
Appl. No.: |
15/840439 |
Filed: |
December 13, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04R 25/405 20130101;
H04R 25/407 20130101; H04R 2430/23 20130101; H04R 25/552
20130101 |
International
Class: |
H04R 25/00 20060101
H04R025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2016 |
DE |
10 2016 225 205.4 |
Claims
1. A method for determining at least one direction of a useful
signal source in an acoustic system having at least a first input
transducer and a second input transducer, which comprises the steps
of: generating, via the first input transducer, a first input
signal from a sound signal from surroundings; generating, via the
second input transducer, a second input signal from the sound
signal; using the first input signal and the second input signal to
form a plurality of angle-dependent directional characteristics
each having a respective fixed central angle and a respective given
angular expansion; examining signal components pertaining to
individual ones of the angle-dependent directional characteristics
for a presence of a useful signal from the useful signal source;
and assigning the respective fixed central angle to the useful
signal source ascertained in a respective angle-dependent
directional characteristic as the direction of the useful signal
source.
2. The method according to claim 1, wherein an angular distance
between two said angle-dependent directional characteristics that
are adjacent in respect of the respective fixed central angle
corresponds to half the respective given angular expansion.
3. The method according to claim 2, wherein for each of the
angle-dependent directional characteristics the respective fixed
central angle and the respective given angular expansion of an
angle-dependent directional characteristic are prescribed by at
least two conditions.
4. The method according to claim 3, wherein the angle-dependent
directional characteristics are each prescribed by a notch-shaped
sensitivity characteristic that is determined by the at least two
conditions, so that the at least two conditions each stipulate the
respective fixed central angle and the respective given angular
expansion of the notch-shaped sensitivity characteristic.
5. The method according to claim 4, which further comprises forming
an acoustic characteristic variable for each of the angle-dependent
directional characteristics from the signal components, wherein
acoustic characteristic variables of the angle-dependent
directional characteristics are used to ascertain the useful signal
in at least one of the angle-dependent directional
characteristics.
6. The method according to claim 5, which further comprises:
comparing the acoustic characteristic variable of the
angle-dependent directional characteristic with a total value of a
corresponding characteristic variable for the first input signal
and/or the second input signal and a relative characteristic
variable for the angle-dependent directional characteristic is
formed as a result; and ascertaining a presence of the useful
signal in at least one of the angle-dependent directional
characteristics from the relative characteristic variable of the
angle-dependent directional characteristics.
7. The method according to claim 6, which further comprises:
comparing relative characteristic variables with one another and/or
with a prescribed limit value; and ascertaining a presence of the
useful signal in at least one of the angle-dependent directional
characteristics from results of the comparing step.
8. The method according to claim 5, which further comprises:
setting the acoustic characteristic variable to be a respective
mean value of a signal level over time; and ascertaining a presence
of the useful signal in the angle-dependent directional
characteristic from an attenuation that the respective mean value
of the signal level over time experiences in the angle-dependent
directional characteristic, normalized using a mean value of a
total level over time, as a result of the notch-shaped sensitivity
characteristic.
9. The method according to claim 4, which further comprises:
providing a further input transducer that generates a further input
signal from the sound signal; and forming the angle-dependent
directional characteristics on a basis of the first input signal,
the second input signal and the further input signal.
10. The method according to claim 9, wherein the angle-dependent
directional characteristics are each provided by a plurality of
conditions that is a same as a number of input signals, so that the
plurality of conditions each stipulate at least the respective
fixed central angle and the respective given angular expansion of
the notched shaped sensitivity characteristic.
11. An acoustic system, comprising: at least one first input
transducer; a second input transducer; and a signal processing unit
programmed to perform a method for determining at least one
direction of a useful signal source in the acoustic system, the
method comprises the steps of: generating, via said first input
transducer, a first input signal from a sound signal from
surroundings; generating, via said second input transducer, a
second input signal from the sound signal; using the first input
signal and the second input signal to form a plurality of
angle-dependent directional characteristics each having a
respective fixed central angle and a respective given angular
expansion; examining signal components pertaining to individual
ones of the angle-dependent directional characteristics for a
presence of a useful signal from a useful signal source; and
assigning the respective fixed central angle to the useful signal
source ascertained in a respective angle-dependent directional
characteristic as the direction of the useful signal source.
12. The acoustic system according to claim 11, wherein the acoustic
system is a hearing device.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit, under 35 U.S.C.
.sctn.119, of German patent application DE 10 2016 225 205.4, filed
Dec. 15, 2016; the prior application is herewith incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The invention relates to a method for determining at least
one direction of a useful signal source in an acoustic system that
contains at least a first input transducer and a second input
transducer. The first input transducer generates a first input
signal from a sound signal from the surroundings and the second
input transducer generates a second input signal from the sound
signal.
[0003] For operation of a hearing device, the algorithms that are
used for user-specific amplification and, more generally, for tone
matching to input signals of the hearing device that are obtained
from the ambient sound often need to be selected on the basis of a
respective hearing situation. In this case, the individual hearing
situations are manifested as frequently recurring patterns of
overlays of interfering sounds or, generally, noise of a useful
signal sound, the patterns being standardized inter alia on the
basis of the type of noise occurring, the signal-to-noise ratio,
the frequency response of the useful signal sound and temporal
variations and mean values of the cited variables.
[0004] On the basis of the identified hearing situation, it is thus
particularly possible for the signal-to-noise ratio in the input
signals to be improved in an efficient and resource-saving manner,
since this achieves a reduction in the noise by means of its
properties that can be expected statistically within the context of
the standardization as a hearing situation.
[0005] Specifically in particularly complicated real acoustic
surroundings--for example with multiple noise sources, which
additionally result in a high total noise level--improving the
sound quality can, however, result in the requirement for the
position of a useful signal source, for example a speaker in a
conversation, to be located directly.
[0006] At present, it is known practice for useful signal sources
to be located in binaural hearing devices by a measurement of the
delay time difference that results from the different propagation
times of a sound signal to the respective hearing aids of the
binaural hearing device that are worn on both ears of the user.
However, such a measurement requires firstly a high level of
computational complexity and secondly the fastest possible and
nevertheless detailed transmission of the signal components from
one hearing aid to the other hearing aid through evaluation. The
two cited requirements adversely affect the power consumption of
the hearing aids.
SUMMARY OF THE INVENTION
[0007] The invention is therefore based on the object of specifying
for an acoustic system a method that locates a useful signal source
as accurately as possible with the lowest possible level of
computational and system complexity.
[0008] The cited object is achieved according to the invention by a
method for determining at least one direction of a useful signal
source in an acoustic system that contains at least a first input
transducer and a second input transducer. The first input
transducer generates a first input signal from a sound signal from
the surroundings and the second input transducer generates a second
input signal from the sound signal. The first input transducer
generates a first input signal from a sound signal from the
surroundings and the second input transducer generates a second
input signal from the sound signal. The first input signal and the
second input signal are used to form a plurality of angle-dependent
directional characteristics having a respective given central angle
and a respective identical angular expansion. The signal components
pertaining to the individual directional characteristics are
examined for the presence of a useful signal from a useful signal
source, and wherein the applicable central angle is assigned to a
useful signal source ascertained in a particular directional
characteristic as the direction of the useful signal source.
Refinements that are advantageous and in some cases inventive in
themselves are the subject matter of the subclaims and the
description that follows.
[0009] In this context, an input transducer generally covers any
acoustoelectric transducer that produces an electrical signal from
a sound signal, that is to say particularly also a microphone.
[0010] Preferably, the individual directional characteristics have
a respective minimum or a respective maximum sensitivity to a test
signal from the applicable angular direction at their respective
central angle. The directional characteristics in this case include
directional lobes, in particular, which have the greatest
sensitivity in the direction of their respective central angle, the
sensitivity decreasing each time the angular distance from the
central angle increases. The extent of the decrease in the
sensitivity as the angular distance from the central angle
increases can be taken as a measure of the angular expansion of the
directional characteristic in this case. Alternatively, the
individual directional characteristics can each also have a minimum
sensitivity to a given test signal at the respective central angle,
the sensitivity to the test signal increasing as the angular
distance from the central angle increases. The extent of the
increase in the sensitivity as the angular distance from the
central angle increases can then be used as a measure of the
angular expansion. Preferably, the central angles of two adjacent
directional characteristics are at a fixed angular distance from
one another. This means that a kind of scan of an angular range is
performed by means of the individual directional characteristics,
the central angle changing by a constant amount in each case in the
event of a transition from one directional characteristic to its
adjacent directional characteristic.
[0011] The examination of the signal components, including the
presence of a useful signal, from a useful signal source can be
effected in the individual directional characteristics,
particularly on the basis of the signal level or on the basis of
one or more variables that are derived from the signal level.
[0012] The assignment of a central angle of a directional
characteristic as the direction of a useful signal source
ascertained in the applicable directional characteristic now has
the advantage that this allows the useful signal source to be
located even in the presence of other useful signal sources, for
example if a new, further useful signal source is added to an
already existent useful signal source with an applicable useful
signal, the further useful signal source being clearly physically
separate from the first, already existent useful signal source. The
detection or location of the individual useful signal sources is
not impaired by the presence of other useful signal sources in this
case, as might occur in the case of a location by use of phase
measurement, where every further useful signal source worsens the
signal-to-noise ratio at least as noise, and therefore could impair
the robustness and also the angular resolution of the locating. In
particular, it is then possible to use permanent application, or
application repeated at short intervals of time, of the locating to
achieve a temporal resolution for the locating of a useful signal
source. This therefore also allows physical tracking of a mobile
useful signal source. The direction of the useful signal source,
which is determined as the result of the method, can be used
particularly to orient a directional lobe to the useful signal
source during the input conversion of the acoustic system, in order
to use the directional lobe to improve the signal-to-noise ratio of
the useful signal source relative to the background noise.
[0013] Preferably, an angular distance between two directional
characteristics that are adjacent in respect of their central angle
corresponds to half the angular expansion. In particular, the two
adjacent directional characteristics in this case have the same
angular expansion. If the individual directional characteristics
are formed by directional lobes whose sensitivity is at a maximum
in the direction of the central angle, and decreases as the angular
distance from the central angle increases, this means particularly
that an angle for which the sensitivity to a test signal has fallen
by a particular factor relative to the maximum value at the central
angle, for example 6 dB or 10 dB, can be specified for every single
directional characteristic. Such an angle is now assigned to the
applicable directional characteristic as half an angular expansion,
and the central angle of the adjacent directional characteristic is
accordingly chosen to be at an angular distance of half an angular
expansion. If notch-shaped attenuations of the sensitivity with a
minimum at the central angle are chosen as individual directional
characteristics in each case, a similar situation can apply, with a
raise of the sensitivity relative to the minimum value at the
central angle being used for the definition of the angular
expansion instead of the attenuation of the sensitivity relative to
the maximum value at the central angle. This allows largely
complete coverage by the individual directional characteristics to
be attained for a desired, wider angular range, whereas overlaps in
the individual directional characteristics up to the next central
angle in each case mean that a useful signal source can always be
clearly assigned to at least one of the directional
characteristics, the overlap also allowing angular positions
between two adjacent central angles to be resolved.
[0014] Advantageously, for each of the individual directional
characteristics the central angle and the angular expansion of the
directional characteristic are determined by at least two
conditions. In particular, the directional characteristics can each
be formed using the "linearly constrained minimum variance" method
on the basis of the conditions. This allows the conditions, for
example in the form of relative attenuations in the sensitivity, to
be oriented in a particular angular direction, and allows the
respective directional characteristics to be formed directly
therefrom.
[0015] It is found to be advantageous if the individual directional
characteristics are each prescribed by a notch-shaped sensitivity
characteristic that is determined by at least two conditions, so
that the at least two conditions each stipulate the central angle
and the angular expansion of the sensitivity characteristic. In
this case, a notch-shaped sensitivity characteristic is intended to
be understood to mean a directional characteristic that has the
maximum attenuation in the sensitivity for a test signal of
prescribed volume at the central angle, the sensitivity increasing
as the angular distance from the central angle increases. The
extent of this increase in the sensitivity on the basis of the
angular distance from the central angle then defines the angular
expansion. If a useful signal source is situated in the direction
of a central angle of such a directional characteristic, or, within
the context of the angular resolution, in direct proximity to the
central angle, that is to say within the "notch" of the sensitivity
characteristic, then the signal components of the useful signal are
substantially attenuated by the directional characteristic, whereas
signal components of other useful signal sources that are situated
outside the angular expansion around the central angle of the
directional characteristic are largely retained. This can now be
used to ascertain a presence of a useful signal source in the
region of the applicable directional characteristic.
[0016] Expediently, an acoustic characteristic variable is formed
for each of the individual directional characteristics from the
signal components, the acoustic characteristic variables of the
directional characteristics are used to ascertain a useful signal
in at least one of the directional characteristics. The acoustic
characteristic variable used in this case can be particularly the
maximum signal level over a suitable time window or the signal
level averaged over the time window, particularly only signal
components in particular frequency bands also being able to be used
for the formation of the acoustic characteristic variables.
[0017] Preferably, in this case, the acoustic characteristic
variable of the directional characteristic is compared with the
total value of the corresponding characteristic variable for the
first input signal and/or the second input signal, and a relative
characteristic variable for the directional characteristic is
formed as a result, wherein the presence of a useful signal in at
least one of the directional characteristics is ascertained from
the relative characteristic variable of the directional
characteristics. This means that the acoustic characteristic
variable, for example a signal level averaged over time, is first
of all formed for each of the individual directional
characteristics, and subsequently the acoustic characteristic
variable of each directional characteristic is normalized using an
appropriate characteristic variable that is derived from the first
input signal and/or from the second input signal. The normalization
then forms for each directional characteristic the relative
characteristic variable that is ultimately used as a measure of the
presence of a useful signal in the directional characteristic. The
characteristic variable used for the normalization can be the
reference level of the first input signal or of the second input
signal or else the total level of the first input signal and the
second input signal, for example. The effect that can be achieved
by the normalization is that in hearing situations in which the
respective sound level or else the number of individual useful
signal sources can change, the resultant changes in the overall
level do not affect the resolution of the locating of the useful
signal sources.
[0018] Preferably, in this case, the relative characteristic
variables are each compared with one another and/or with a
prescribed limit value, and the presence of a useful signal in at
least one of the directional characteristics is ascertained
therefrom. The comparison of the relative characteristic variables
with one another is found to be advantageous to the effect that it
allows the presence of a useful signal in the applicable
directional characteristic to be inferred directly from an extreme
value (maximum or minimum) of a relative characteristic variable,
depending on the nature of the directional characteristics. To
locate a plurality of useful signal sources, however, it may also
be advantageous to compare the relative characteristic variables
with a prescribed limit value that, when exceeded or fallen below,
allows the presence of a useful signal source to be inferred.
[0019] It is found to be advantageous if the characteristic
variable used is a respective mean value of the signal level over
time, and the presence of a useful signal in a directional
characteristic is ascertained from an attenuation that the mean
value of the signal level over time experiences in the directional
characteristic, normalized using the mean value of the total level
over time, as a result of the respective sensitivity
characteristic. The time window for the averaging can be dependent
particularly on the nature of the useful signal sources that is to
be expected. If at least one of the useful signal sources is an
interlocutor, for example, then the time window can preferably be
chosen such that particular frequency bands, e.g. format
frequencies, are excited to a sufficiently high degree.
[0020] In an advantageous refinement, a further input transducer
generates a further input signal from the sound signal, wherein the
directional characteristics are formed on the basis of the first
input signal, the second input signal and the further input signal.
Preferably, the further input transducer is physically separate
from the first input transducer and from the second input
transducer in this case. The addition of the further input signal
increases the total available phase information about the sound
signal, so that the directional characteristics can be used to
achieve a higher angular resolution.
[0021] It is found to be particularly advantageous in this case if
the individual directional characteristics are each provided by a
plurality of conditions that is the same as the number of input
signals, so that the plurality of conditions each stipulate at
least the central angle and the angular expansion. This means that,
in the case of four input signals from four physically separate
input transducers, for example, the individual directional
characteristics can each be stipulated by up to four conditions.
This allows particularly narrow angular expansions and therefore a
particularly high angular resolution to be attained.
[0022] The invention further cites an acoustic system, containing
at least one first input transducer for producing a first input
signal from a sound signal from the surroundings, a second input
transducer, a second input transducer for producing a second input
signal from the sound signal, and a signal processing unit that is
set up to perform the method described above. In particular, the
acoustic system is configured as a hearing device. The advantages
cited for the method and the developments thereof can be
transferred mutatis mutandis to the acoustic system in this
case.
[0023] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0024] Although the invention is illustrated and described herein
as embodied in a method for determining a direction of a useful
signal source, it is nevertheless not intended to be limited to the
details shown, since various modifications and structural changes
may be made therein without departing from the spirit of the
invention and within the scope and range of equivalents of the
claims.
[0025] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0026] FIGS. 1A and 1B are plan views of a hearing situation for a
user of a binaural hearing device in which the number of
interlocutors for the user changes;
[0027] FIG. 2 is a block diagram of a sequence of a method for
determining a direction of a useful signal source;
[0028] FIG. 3 is a plan view of a directional characteristic of the
hearing device shown in FIGS. 1A and 1B at a given central angle
and a given angular expansion; and
[0029] FIG. 4 is a graph showing a profile of relative
characteristic variables for locating a speaker for a hearing
situation as shown in FIG. 1A and 1B over a time axis.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Mutually corresponding parts and variables are each provided
with the same reference symbols in all the figures.
[0031] Referring now to the figures of the drawings in detail and
first, particularly to FIGS. 1A and 1B thereof, there is shown
schematically a plan view of a hearing situation 1. In the
left-hand depiction, namely FIG. 1A, a user 2 of an acoustic system
4, which in the present case is configured as a binaural hearing
device, is in a conversation with a first interlocutor 6, who is
positioned at the front relative to the line of vision of the user
2, that is to say is standing at an angle of 0 degrees relative to
the user 2. For this hearing situation 1, the binaural hearing
device has located the position of the interlocutor 6 as part of
its resolution options. After some time in the conversation, a
second interlocutor 8 now joins, which results in a new hearing
situation 1', see FIG. 1B. The second interlocutor 8 is positioned
approximately at an angle of -45 degrees relative to the line of
vision of the user 2. If a directional characteristic oriented to
the first interlocutor 6 is now formed in the binaural hearing
device, for example to better amplify the original signal, that is
to say the signal from the first interlocutor 6, then components of
the conversation of the second interlocutor 8 are rejected or are
not sufficiently captured by such a directional characteristic. So
as now to be able to perform direction-dependent rejection of
background noise in the changed hearing situation 1', and also not
to substantially rejected contributions to the conversation by the
second interlocutor 8 relative to those of the first interlocutor
6, it is of considerable advantage to locate the position of the
second interlocutor 8 as accurately as possible.
[0032] FIG. 2 depicts a block diagram of the sequence of a method
10 for determining a direction of a useful signal source in an
acoustic system 4. In the present case, the useful signal source is
provided by the first interlocutor 6 or the second interlocutor 8
in one of the two hearing situations 1, 1' which are in FIGS. 1A
and 1B. The acoustic system 4 is formed by a binaural hearing
device in the present case. The binaural hearing device contains a
first local unit 12 and a second local unit 14, which can each be
worn on the left or right ear of the user 2 when the binaural
hearing device is used as intended. The first local unit 12 or the
second local unit 14 has a first input transducer 16 or a second
input transducer 18 that generates a first input signal 20 or a
second input signal 22 from a respective incoming sound signal from
the surroundings. The first input transducer 16 and the second
input transducer 18 are each provided by a microphone in the
present case. If need be, a further input transducer 19 may also be
provided that produces a further input signal 23.
[0033] For a plurality of central angles .alpha.j, which cover the
front hemisphere of the user 2 in steps of 15 degrees in both
directions starting from 0 degrees, a first filter parameter
F1(.alpha.j) and a second filter parameter F2(.alpha.j) are now
each defined on the basis of two conditions B1, B2. The first
filter parameter F1(.alpha.j) and the second filter parameter
F2(.alpha.j) are in this case of a nature such that they form a
notch-shaped sensitivity characteristic 24 by convolution with the
first input signal 20 or the second input signal 22 in a manner yet
to be described. If the first input signal 20 and the second input
signal 22 are thus each filtered using the first filter parameter
F1(.alpha.j) or the second filter parameter F2(.alpha.j), then the
sum of the resultant signals has a much lower sensitivity for
signal components whose signal source is in the direction of the
central angle .alpha.j of the sensitivity characteristic 24 than
for signals whose signal source is in another direction. For the
signal 26 resulting from the filtering described, an acoustic
characteristic variable 28 is now formed by virtue of the signal
level of the resultant signal 26 being averaged over a prescribed
interval of time. The acoustic characteristic variable 28 formed
from the averaged signal level is normalized using a reference
level 30, and in this way a relative characteristic variable 32 is
formed. In the present case, the reference level 30 is provided by
a mean value of the level of the first input signal 16 over time.
Alternatively, the reference level 30 used may also be a mean value
of the overall level over time, that is to say of the level of the
sum of the first input signal 16 and the second input signal 18.
The relative characteristic variables 32 thus formed for a central
angle .alpha.j are now each compared with one another. In the
comparison 34, each central angle .alpha.j whose sensitivity
characteristic 24 has the relative characteristic variable 32 with
the lowest value is now stipulated as the direction of a useful
signal source.
[0034] FIG. 3 depicts a plan view of a directional characteristic
34 with a central angle .alpha.j=-10 degrees and a prescribed
expansion .DELTA.. In this case, the directional characteristic is
formed by a sensitivity characteristic 24 whose central angle
.alpha.j is defined by the direction having the lowest sensitivity.
The concepts of "linearly constrained minimum variants" directional
characteristics (LCMV) can be used to define each of the central
angle .alpha.j and the expansion .DELTA. by means of a given
attenuation of the signal components at the central angle .alpha.j
itself and at a further angle. In the present case, the angular
expansion .DELTA. is determined by virtue of the signal level being
attenuated by 20 dB at a central angle .alpha.j of -10 degrees, and
the signal level being attenuated by 6 dB in the frontal direction,
that is to say at 0 degrees. This defines a notch-shaped
sensitivity characteristic 24 that has substantially lower
sensitivity for signals whose source is in the region of the
central angle .alpha.j, and rejects such signals accordingly.
[0035] If the signal level averaged over time is now first of all
formed method depicted in FIG. 2 for a signal whose signal source
is in the direction of the central angle .alpha.j=-10 degrees, that
is to say in the case of an accordingly positioned interlocutor,
for example, according to the sensitivity characteristic 24, then
the signal level has the lowest possible value as acoustic
characteristic variable 28 for the present signal source of all the
angle-dependent sensitivity characteristics 24. The acoustic
characteristic variable 28 obtained in this manner is now
normalized using the total level averaged over time or the level of
one of the two input signals 20, 22 averaged over time. This
results, in the event of a speaker, that is to say a useful signal
source, being absent in the region of the central angle .alpha.j,
in all contributions being captured for normalization essentially
even without attenuation in the acoustic characteristic variable
28. Only when a useful signal source is present in the region of
the central angle .alpha.j is the contribution of the useful signal
to the acoustic characteristic variable 28 substantially rejected
by the sensitivity characteristic 24, whereas the contribution to
the normalization by the useful signal is retained. The
corresponding decrease in the relative characteristic variable 32
then allows the presence of a useful signal source in the direction
of the central angle .alpha.j to be safely inferred.
[0036] FIG. 4 depicts the relative characteristic variables 32a to
32c for each of three different central angles over a time axis t,
the characteristic variables being assignable to the hearing
situations 1, 1' depicted in FIG. 2. Up to a time of approximately
4.5 seconds, the user 2 is only in conversation with the first
interlocutor 6. The relative characteristic variables 32a to 32c ,
which are formed in a prescribed manner for sensitivity
characteristics with central angles of -30 degrees (32a), -45
degrees (32b) and -60 degrees (32c), consequently have no kind of
reference points for a useful signal source in the applicable
angular range. At approximately 4.5 seconds, the transition from
hearing situation 1 to hearing situation 1' now occurs, the second
interlocutor 8 joins and, in so doing, makes contributions to the
conversation that now enter the processes described above as a
sound signal. The contributions to the conversation by the second
interlocutor 8 and the further presence of the first interlocutor 6
mean that the normalization changes first of all for each of the
three relative characteristic variables 32a to 32c depicted. The
most distinct attenuation of the contribution of the second
interlocutor 8 is effected, as expected, by the sensitivity
characteristic with the central angle at -45 degrees, so that the
relative characteristic variable 32b accordingly also adopts the
lowest value therefor. For the other two central angles -30 degrees
and -60 degrees, the applicable sensitivity characteristics mean
that a certain attenuation of the voice activity of the second
interlocutor 8 still takes place. However, this attenuation is no
longer as pronounced as in the case of the sensitivity
characteristic at -45 degrees. Accordingly, a drop in the value can
be seen in the relative characteristic variables 32a and 32c ,
which does not approach the reduction from -45 degrees (32b),
however. From this, it is now possible to infer the joining of the
second interlocutor 8 at approximately 4.5 seconds at an angle of
-45 degrees.
[0037] Although the invention has been illustrated and described in
more detail by the preferred exemplary embodiment, the invention is
not limited by this exemplary embodiment. Other variations can be
derived therefrom by a person skilled in the art without departing
from the scope of protection of the invention.
[0038] The following is a summary list of reference numerals and
the corresponding structure used in the above description of the
invention: [0039] 1 Hearing situation [0040] 2 User [0041] 4
Acoustic system [0042] 6 First interlocutor [0043] 8 Second
interlocutor [0044] 10 Method [0045] 12 First local unit [0046] 14
Second local unit [0047] 16 First input transducer [0048] 18 Second
input transducer [0049] 19 Further input transducer [0050] 20 First
input signal [0051] 22 Second input signal [0052] 23 Further input
signal [0053] 24 Sensitivity characteristic [0054] 26 Resultant
signal [0055] 28 Acoustic characteristic variable [0056] 30
Reference level [0057] 32 Relative characteristic variable [0058]
32a-c Relative characteristic variable [0059] 34 Directional
characteristic [0060] B1, B2 Condition [0061] F1 First filter
parameter [0062] F2 Second filter parameter [0063] .alpha.j Central
angle [0064] .DELTA. Expansion
* * * * *